Browsing by Author "Santos, A.C.T."
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- Assessment of metal and metalloid contamination in soils trough compositional data: the old Mortórios uranium mine area, central PortugalPublication . Neiva, A.M.R.; Albuquerque, M.T.D.; Antunes, I.M.H.R.; Carvalho, Paula; Santos, A.C.T.; Boente, Carlos; Cunha, Pedro Proença; Henriques, S.B.A.; Pato, R.L.Soils from the old Mortórios uranium mine area were studied to look for contamination, as they are close to two villages, up to 3 km away, and used for agriculture. They are mainly contaminated in U and As and constitute an ecological threat. This study attempts to outline the degree to which soils have been affected by the old mining activities through the computation of significant hot clusters, Traditional geostatistical approaches commonly use raw data (concentrations) accepting that the analyzed elements represent the soil's entirety. However, in geochemical studies these elements are just a fraction of the total soil composition. Thus, considering compositional data is pivotal. The spatial characterization, considering raw and compositional data together, allowed a broad discussion about not only the concentrations' spatial distribution, but also a better understanding on the possibility of trends of "relative enrichment" and, furthermore an insight in U and As fate. The highest proportions (compositional data) on U (up to 33%), As (up to 35%) and Th (up to 13%) are reached in the south-southeast segment. However, the highest concentrations (raw data) occur in north and northwest of the studied area, pointing out to a "relative enrichment" toward the south-southeast zone. The Mondego Sul area is mainly contaminated in U and As, but also in Co, Cu, Pb and Sb. The Mortórios area is less contaminated than the Mondego Sul area.
- Contaminação ambiental provocada pela antiga mina de urânio de Pinhal do Souto, centro de PortugalPublication . Neiva, A.M.R.; Carvalho, Paula; Antunes, I.M.H.R.A.; Silva, M.M.V.G.; Santos, A.C.T.; Pinto, M.M.S.C.; Cunha, Pedro ProençaA mina de urânio de Pinhal do Souto foi explorada subterraneamente entre 1978 e 1989, tendo produzido 93091 kg de U3O8. Na área ficaram duas escombreiras, parcialmente cobertas por vegetação natural. Nesta mina foi explorado um filão de quartzo contendo autunite e torbernite, que corta um granito de duas micas. A mina está a causar contaminação em U, As, Cd, Cr, Cu, Fe, Ni e Pb nas águas, em Cr, Mn, Pb, Cd, Co, Fe, Th, Zn e, por vezes, em U nos sedimentos de corrente e em Cu, Pb, Zn, As, Cd e Sb nos solos. Os valores da mediana de Fe, As, Cd, Pb, Sb, Th, U, W e Zn destes solos são superiores aos dos solos dos países europeus dos dados FOREGS. forma complexos com nas águas que têm pH neutro a alcalino. As concentrações de U na água são superiores aos limites para uso humano nas épocas húmida e seca, mas são maiores na época húmida por os minerais secundários de U se dissolverem e o U ser libertado na água. Os teores de metais e As são maiores na água da época seca devido à evaporação. Os solos têm vermiculite e, por isso, retêm maiores concentrações de metais do que os sedimentos de corrente que possuem caulinite. Devido aos valores de pH ligeiramente ácidos a neutros das águas, há a ocorrência de precipitados de óxido de Fe, sobretudo nas saídas de galerias subterrâneas, que são ricos em óxidos-hidróxidos e matéria orgânica e que retêm grandes quantidades de metais U, Th e As.
- Contaminated water, stream sediments and soils close to the abandoned Pinhal do Souto uranium mine, central PortugalPublication . Neiva, A.M.R.; Carvalho, Paula; Antunes, I.M.H.R.; Silva, M.M.V.G.; Santos, A.C.T.; Pinto, M.M.S.C.; Cunha, Pedro ProençaThe Pinhal do Souto mine exploited a quartz vein containing uranium minerals, mainly autunite and torbernite. This vein intersects a two-mica granite containing 10 ppm U and uraninite. The mine was exploited underground and produced 93091 kg U3O8 between 1978 and 1989 and was then closed down. Two dumps were left in the mine area and these are partially covered by natural vegetation. Groundwater and surface water have a similar slightly acid-to-alkaline pH. The 2 2 UO is abundant and complexed with 2 3 CO , under neutral to alkaline pH. Metals and arsenic concentrations in the water increase during the dry season due to the evaporation. Uranium concentration in the water increases (up to 104.42 g/l) in the wet season, because secondary uranium minerals are dissolved and uranium is released into the water. Soils tend to retain a higher concentration of several metals, including U (up to 336.79 mg/kg) than stream sediments (up to 35.68 mg/kg), because vermiculite from the former could adsorb it more easily than could kaolinite from the latter. The Fe-oxides precipitate retains the highest concentrations of several metals, including U and Th (up to 485.20 and 1053.12 mg/kg, respectively) and the metalloid As, because it is richer in oxyhydroxides and organic matter than stream sediments and soils. The median concentrations of Fe, As, Cd, Pb, Sb, Th, U, W and Zn in soils from this area are higher than in European soils of the FOREGS data. Waters from dry and wet seasons, stream sediments and soils are contaminated and must not be used. This area was compared with another Portuguese abandoned uranium mine area. The former mine caused a lower environmental impact attributable to it having lower sulfide concentration and mineral alteration than in the latter.
- Mobility of uranium in groundwater-surface water systems in a post-mining context (Central Portugal)Publication . Antunes, I.M.H.R.; Carvalho, Paula; Albuquerque, Maria Teresa; Santos, A.C.T.In uranium abandoned mine areas, particularly with mine tailings and open-pit lakes, the mobility of potentially toxic elements still acts as a source of surface and groundwater contamination. e water of open-pit lakes from Ribeira de Bôco mine and associated groundwater and surface water from the area is neutral and with low metal contents. However, some water samples are contaminated with Cd, Cr, Cu, Fe, Mn, As, and U and should not be used for human consumption or in agricultural activities. e baseline uranium threshold is considerably high for groundwater, which is supported by geogenic features and mining activities.
- Potential toxic elements in stream sediments, soils and waters in an abandoned radium mine (central Portugal)Publication . Antunes, I.M.H.R.; Neiva, A.M.R.; Albuquerque, M.T.D.; Carvalho, Paula; Santos, A.C.T.; Cunha, Pedro ProençaThe Alto da Várzea radium mine (AV) exploited ore and U-bearing minerals, such as autunite and torbernite. The mine was exploited underground from 1911 to 1922, closed in 1946 without restoration, and actually a commercial area is deployed. Stream sediments, soils and water samples were collected between 2008 and 2009. Stream sediments are mainly contaminated in As, Th, U and W, which is related to the AV radium mine. The PTEs, As, Co, Cr, Sr, Th, U, W, Zn, and electrical conductivity reached the highest values in soils collected inside the mine influence. Soils are contaminated with As and U and must not be used for any purpose. Most waters have pH values ranging from 4.3 to 6.8 and are poorly mineralized (EC = 41–186 µS/cm; TDS = 33–172 mg/L). Groundwater contains the highest Cu, Cr and Pb contents. Arsenic occurs predominantly as H2(AsO4)− and H(AsO4)2−. Waters are saturated in goethite, haematite and some of them also in lepidocrocite and ferrihydrite, which adsorbs As (V). Lead is divalent in waters collected during the warm season, being mobile in these waters. Thorium occurs mainly as Th(OH)3(CO3)−, Th(OH)2(CO3) and Th(OH)2(CO3)22−, which increase water Th contents. Uranium occurs predominantly as UO2CO3, but CaUO2(CO3)32− and CaUO2(CO3)3 also occur, decreasing its mobility in water. The waters are contaminated in NO2−, Mn, Cu, As, Pb and U and must not be used for human consumption and in agricultural activities. The water contamination is mainly associated with the old radium mine and human activities. A restoration of the mining area with PTE monitoring is necessary to avoid a public hazard
- Spatial and temporal variability of surface water and groundwater before and after the remediation of a Portuguese uranium mine areaPublication . Neiva, A.M.R.; Carvalho, Paula; Antunes, I.M.H.R.; Santos, A.C.T.; Pinto, M.M.S.C.The old Senhora das Fontes uranium mine, in central Portugal, consists of quartz veins which penetrated along fracture shear zones at the contact between graphite schist and orthogneiss. The mine was exploited underground until a depth of 90 m and was closed down in 1971. The ores from this mine and two others were treated in the mine area by the heap-leach process which ended in 1982. Seven dumps containing a total of about 33,800 m3 of material and partially covered by natural vegetation were left in the mine area. A remediation process took place from May 2010 to January 2011. The material deposited in dumps was relocated and covered with erosion resisting covers. Surface water and groundwater were collected in the wet season just before the remediation, in the following season at the beginning of the remediation and also after the remediation in the following dry season. Before, at the beginning and after the remediation, surface water and groundwater have an acid-to-alkaline pH, which decreased with the remediation, whereas Eh increased. In general, before the remediation, uranium concentration was up to 83 μg/L in surface water and up to 116 μg/L in groundwater, whereas at the beginning of the remediation it increases up to 183 μg/L and 272 μg/L in the former and the latter, respectively, due to the remobilization of mine dumps and pyrite and chalcopyrite exposures, responsible for the pH decrease. In general, after the remediation, the U concentration decreased significantly in surface water and groundwater at the north part of the mine area, but increased in both, particularly in the latter up to 774 μg/L in the south and southwest parts of this area, attributed to the remobilization of sulphides that caused mobilization of metals and arsenic which migrated to the groundwater flow. Uranium is adsorbed in clay minerals, but also in goethite as indicated by the geochemical modelling. After the remediation, the saturation indices of oxyhydroxides decrease as pH decreases. The remediation also caused decrease in Cd, Co, Cr, Ni, Pb, Zn, Cu, As, Sr and Mn concentrations of surface water and groundwater, particularly in the north part of the mine area, which is supported by the speciation modelling that shows the decrease of most dissolved bivalent species. However, in general, after the remediation, Th, Cd, Al, Li, Pb, Sr and As concentrations increased in groundwater and surface water at south and southwest of the mine area. Before and after the remediation, surface water and groundwater are contaminated in U, Cd, Cr, Al, Mn, Ni, Pb, Cu and As. Remediation caused only some improvement at north of the mine area, because at south and southwest part, after the remediation, the groundwater is more contaminated than before the remediation.
- Spatial surface and groundwater interaction in an abandoned radium-bearing mine (Guarda, Central Portugal)Publication . Antunes, I.M.H.R.; Neiva, A.M.R.; Albuquerque, M.T.D.; Santos, A.C.T.The abandoned Alto da Várzea radium mine exploited quartz veins containing ore minerals and U-bearing minerals, such as autunite and torbernite. The area is located on a Variscan two-mica granite that intruded the schist–greywacke complex. The mine was exploited underground from 1911-22 and was closed down in 1946. This mine was not restored and actually a commercial area is deployed.A total of ten surface water and groundwater samples were collected in the study area between 2008/09. Most water samples have pH values ranging from 4.3 to 6.8 and are poorly mineralized (EC=41-186 μ S/cm; TDS=33-172 mg/L). However, the waters are contaminated with NO2-, Mn, Cu, As and U and must not be used for human consumption and some of them in agricultural activities. The water contamination is mainly associated with the old radium mine and human activities developed in the area.